High density materials have been made for many years. Lead has been commonly used in applications requiring a high density material. Applications of high density materials include shotgun pellets, other ballistic projectiles, fishing lures, fishing weights, wheel weights and other high density applications. As an example, lead has also been used in applications requiring properties other than density including in radiation shielding because of its resistance to α, β and γ radiation, EMI and malleability characteristics. Press-on fishing weights made of lead allow the user to easily pinch the weight onto a fishing line without tools or great difficulty. In the case of shotgun pellets, or other ballistic projectiles, lead offers the required density, penetrating force and malleability to achieve great accuracy and minimum gun barrel wear. Lead has been a primary choice of both hunting and military applications. Many jurisdictions in the United States and elsewhere have seriously considered bans on the sale and use of lead shot and lead sinkers due to increasing concentrations of lead in lakes and resulting mortality in natural populations. Other high-density materials such as depleted uranium have been proposed and implemented.
Composite materials have been suggested as a replacement for lead and other high-density materials. Composite materials have been made for many years by combining generally two dissimilar materials to obtain beneficial properties from both. A true composite is unique because the interaction of the materials provides the best properties of both components. Many types of composite materials are known and are not simple admixtures. Generally, the art recognizes that combining metals of certain types and at proportions that form an alloy provides unique properties in metal/metal alloy materials. Metal/ceramic composites have been made typically involving combining metal particulate or fiber with clay materials that can be fired into a metal/ceramic composite.
Combining typically a thermoplastic or thermoset polymer phase with a reinforcing powder or fiber produces a range of filled materials and, under the correct conditions, can form a true polymer composite. A filled polymer, with the additive as a filler, cannot display composite properties. A filler material typically is comprised of inorganic materials that act as either pigments or extenders for the polymer systems. A vast variety of fiber-reinforced composites have been made typically to obtain fiber reinforcement properties to improve the mechanical properties of the polymer in a unique composite.
Metal polymer admixtures in which a finely divided metallic material, a metal powder or fiber is dispersed in a polymer have been suggested. One subset of filled polymer materials is metal polymer admixtures in which a metallic material, a metal particulate or fiber is dispersed in a polymer. The vast majority of these materials are admixtures and are not true composites. Admixtures are typically easily separable into the constituent parts and display the properties of the components. A true composite resists separation and displays enhanced properties of the input materials. A true composite does not display the properties of the individual components. Tarlow, U.S. Pat. No. 3,895,143, teaches a sheet material comprising elastomer latex that includes dispersed inorganic fibers and finely divided metallic particles. Bruner et al., U.S. Pat. No. 2,748,099, teach a nylon material containing copper, aluminum or graphite for the purpose of modifying the thermal or electrical properties of the material, but not the density of the admixture. Sandbank, U.S. Pat. No. 5,548,125, teaches a clothing article comprising a flexible polymer with a relatively small volume percent of tungsten for the purpose of obtaining radiation shielding. Belanger et al., U.S. Pat. No. 5,237,930, disclose practice ammunition containing copper powder and a thermoplastic polymer, typically a nylon material. Epson Corporation, JP 63-273664 A shows a polyamide containing metal silicate glass fiber, tight knit whiskers and other materials as a metal containing composite. Bray et al., U.S. Pat. Nos. 6,048,379 and 6,517,774, disclose an attempt to produce tungsten polymer composite materials. The patent disclosures combine tungsten powder having a particle size less than 10 microns, optionally with other components and a polymer or a metal fiber. The materials sold by the Bray et al. assignee and the materials disclosed in the patent do not attain a density greater than 10.0 gm-cm−3.
While a substantial amount of work has been done regarding composite materials generally, high density metal composite materials have not been obtained having a density greater than 10 grams-cm−3, where density is a single measurement to illustrate the composite property. Increasing the density of these materials introduces unique mechanical properties into the composite and, when used, obtains properties that are not present in the lower density composite materials. A substantial need exists for an extrudable material that has high density, low toxicity, and improved properties in terms of electrical/magnetic properties, malleability, thermal processability, particularly using existing thermal processing equipment, and viscoelastic properties.